In the field of the disclosure, a plurality of types of double-tray orthoses have been proposed in the prior art.
In particular, an orthosis as described by the patent document FR 2 820 307 is known, formed by two trays in a general U shape, namely a lower so-called mandibular tray and an upper so-called maxilla tray, each of which has individual tooth cells and comprising projecting elements with complementary shapes, capable of engaging with one another to ensure the connection of the trays. The projecting elements are of the mortise and tenon type, preferably with a dovetail.
It is thus possible to attach the lower tray with the upper tray with a possible adjustment in the anteroposterior direction.
This solution has, in particular, the following disadvantages:                the projecting elements with engagement by resilient deformation do not enable a reliable connection, and the user may thus separate the lower tray from the upper tray, then put them back together in a possibly inappropriate position;        the projecting elements by simple assembly or by bonded assembly do not ensure that the upper and lower trays will remain permanently secured when the device is placed in the mouth, thereby making the retainer inoperative;        in a possible mass production by plastic injection, the mortise and tenon system may be expensive to industrialize.        
Another orthosis described by the patent document published under number WO 03/034957 is known, which describes an intra-oral orthosis including:                an upper tray and a lower tray intended to respectively cover the teeth of an upper jaw and the teeth of a lower jaw;        two ties retaining the trays, which ties have a length so that the lower jaw is held in an advanced position with respect to the upper jaw.        
In this solution, the ties have means enabling their length to be adjusted. A number of solutions are proposed for producing ties with a variable length, namely:                the ties have two threaded passages in which a rod is screwed, the ends of which have a reverse pitch, with a nut being placed at the center of the rod;        the ties include a cylinder in which a rod having an end including a piston slides under the action of a hydraulic pressure;        the ties include two bars sliding one into the other, each being equipped with a drilling.        
Such solutions have, in particular, the following disadvantages:                the ties are small mechanical parts, requiring relatively precise machining, which tends to make the production of ties expensive;        the ties may have projecting portions capable of causing small cuts in the person wearing the orthosis.        